Appomattox

Pre-qualifying fiber ropes for deepwater mooring

Challenge

Deepwater is an important segment of the oil and gas industry and holds vast potential. However, deepwater projects are capital intensive and consequently operators are looking for ways of reducing the cost. Shell has developed the Appomattox (APX) field located in the Gulf of Mexico. The Appomattox semi-submersible is featuring a chain-polyester-chain mooring system. 

DNV solution

• In order to select and optimize the design of the mooring components, Shell developed a pre-qualification test plan that involved the testing of sub-ropes and full-size ropes from several polyester rope manufacturers
• The entire testing activities related to this pre-qualification programme were carried out at DNV testing facilities in Bergen, Norway, early 2014.

Outcome and benefits

• The tension-elongation characteristics of the polyester ropes, as well as the permanent non-recoverable elongation derived from the pre-qualification testing programme, were used in the early stages of the mooring system’s design
• The pre-qualification programme contributed to Shell’s effort to reduce total project costs, and savings for Shell are estimated on the order of 1-2 million USD in steel chain cost and 1 million USD in mooring system installation time.